It has been suggested that chylomicrons or their remnants are atherogenic. Chylomicrons carry dietary cholesterol into the bloodstream and these particles are degraded by the enzyme lipoprotein lipase in contact with the endothelium. After chylomicron triglyceride hydrolysis, chylomicron remnants, which are enriched in cholesteryl ester, may enter the vessel wall directly for uptake by arterial smooth muscle cells. Alternatively, circulating chylomicron remnants may be taken up by monocyte macrophages prior to their normal clearance by the liver. In both cases, foam cells may result which could contribute to the early stages of atherosclerotic lesions. Therefore, the absolute level of chylomicrons and their remnants and their residency time in plasma may correlate with atherosclerosis. Typical lipoprotein measurements are done 10-12 hours after eating. The post-prandial events related to chylomicron metabolism in most cases would be undetected by these measurements. Our goal is to develop and apply a test which can measure chylomicron and chylomicron remnant clearance to see if abnormalities in this process correlate with fasting lipoprotein abnormalities associated with premature atherosclerosis as well to study the genetic determinants of this process in healthy subjects.